A novel solid-state joining approach was proposed, demonstrating the feasibility of effectively joining refractory metals at relatively low temperatures. Employing advanced characterization techniques, the underlying mechanisms governing the bonding of tantalum (Ta) and titanium (Ti) were systematically investigated. The results reveal that Ta−Ti metallurgical bonding occurs at a peak temperature of approximately 600 °C, representing 18.15% and 32.61% of the melting points of Ta and Ti, respectively. Ultrasonic vibrations can facilitate the phase transformation of Ti from hexagonal close-packed (HCP) α-Ti to body-centered cubic (BCC) β-Ti, effectively enhancing its plasticity and enabling mechanical interlocking with Ta. Additionally, ultrasonic vibrations can promote atomic diffusion at the Ta−Ti interface, leading to the formation of a transition layer with a thickness ranging from 0.3 to 0.8 μm at the bonding interface, which substantially improves the bonding strength of Ta−Ti joint.